Oops, just saw your post, we posted at the same time.
I'm afraid if you open some of the files in Notepad you'll see they've been overwritten with junk. It's probably not possible to recover the project. Sorry :(
We fixed a couple of possible-project-corruption bugs in r51, released a week ago. I'm afraid you may have run in to a bug that was already fixed. I would encourage you to always stay up to date to reduce the chance of you running in to issues like this!